1. Field of the Invention
This invention relates to a small printer, and more particularly to a small printer constructed so as to be capable of effecting printing in two different colors.
2. Description of the Prior Art
With the conventional small printers used in electronic desk-top calculators, it has not been possible that ink ribbons of two colors are provided so that during printing, the positions of the ink ribbons are shifted to enable printing in two colors to be done in accordance with the colors of the ink ribbons.
Printing in two colors in particularly effective is the case where the result of a calculation is negative (-) such as 123,000-223,000=-100,000 as shown in FIG. 1(A) of the accompanying drawings. That is, in such a case, when the result of a calculation is negative (-) and has been printed only in the same ink and therefore, there has been no other way to detect a negative result other than visually confirming the sign (-). FIG. 1(B) of the accompanying drawings shows the printing format effected in the same color, for example, violet, in such a case.
Accordingly, in such a case where printing is effected in the same color, making an oversight of the sign (-) would be fatal. Particularly, in shops or stores where the sales for each day are continuously printed on a roll of paper, the amount of printing would be enormous and summing up the sales for each day would require much labor and time.
However, if, as shown in FIG. 1(C) of the accompanying drawings, the sign and the result of calculation are printed in a different color such as, for example, red, when the result of calculation is negative (-), it would be very easy to judge the result. This would also be excellent engineering advancement.
On the other hand, where the number of printed digits is nine and an attempt is made to indicate a number of nine figures using a conventional printing type belt, there will result a printing format such as "1 2 3 4 5 6 7 8 9" as shown in FIG. 2A without demarcation of every three figure units. In such a case, if an attempt is made to print the number with a space provided at every three figures, two figures cannot be printed as indicated by dotted lines in FIG. 2B of the accompanying drawings because the number of total print figures is nine. In such a case, if a design is made such that the marks "," can be printed without a space being provided to separate each unit as shown in FIG. 2C of the accompanying drawings, all three figure units can be seen and seen at a glance.
Also, assuming that the position whereat printing is effected by a printing type drum D is A as shown in FIG. 3A of the accompanying drawings and if the angle .beta. formed between the position B of a character printed after printing and printing paper C and the straight line L passing through the point B and the upper surface of the printing type drum D, the angle .beta. being called the visibility angle, is small, then the printing type drum D will obstruct the view of the printed character.
Generally, to make this visibility angle .beta. great, the diameter of the printing type drum may be made small and therefore, the printing type drum is constructed as small as possible. However, making the printing type drum small would cause characters printed thereby to be small and would reduce the quality of printing. Therefore, usually, the amount of paper feed P is increased as shown in FIG. 3B of the accompanying drawings to thereby increase the visibility angle .beta., whereas increasing the amount of paper feed P would increase the amount of consumption of paper and is very uneconomical.
Therefore, if a character printed at P.sub.1 is moved to a point P.sub.2 as shown in FIG. 3C of the accompanying drawings, the visibility angle .beta. will become very great. If, thereafter, the printed character is moved back to a point P.sub.3 during the next cycle of printing, the amount of consumption of paper will be reduced.
For example, if P.sub.1 =0 mm and P.sub.2 =25 mm and the distance from P.sub.2 to P.sub.3 is 20 mm, then the amount of consumption of paper will be only 5 mm.